Involvement of prostaglandin E receptor subtype EP4 in head and neck squamous cell carcinoma (HNSCC)

5890 Increased levels of PGE 2 have been detected in a variety of malignancies including HNSCC. Several lines of evidence, beyond the finding of elevated levels of PGE 2 in tumors, suggest that PGE 2 plays a role in tumor growth. For example, PGE 2 can stimulate cell proliferation, cell motility and angiogenesis while inhibiting apoptosis and immune surveillance. Treatment with anti-PGE 2 monoclonal antibody has been reported to suppress the growth of transplantable HNSCC in experimental animals. PGE 2 elicits cellular responses via interaction with four cell surface receptors, EP 1-4 . In this study, we first investigated the expression of EP 1-4 in human HNSCC and then attempted to identify which EP receptor was responsible for mediating the growth of experimental HNSCC. Real-time PCR indicated that each of the four EP receptors was commonly expressed in human HNSCC and in 1483 cell xenografts, a transplantable model of HNSCC. Treatment with ONO-8713, an EP 1 receptor antagonist (RA), did not suppress the growth of 1483 cell xenografts. In contrast, ONO-AE3-208, an EP 4 receptor antagonist (EP 4 RA), caused dose-dependent inhibition of xenograft growth. At a dose of 500 ppm, ONO-AE3-208 caused more than a 50% reduction in tumor growth. Because EP 4 receptor signaling is mediated by the cAMP/protein kinase A (PKA) pathway, levels of cAMP and PKA activity were measured. Treatment with the EP 4 RA caused a reduction in both amounts of cAMP and PKA activity in 1483 xenografts. Immunohistochemistry was performed to elucidate the mechanism underlying the anti-tumor activity of the EP 4 RA. Treatment with ONO-AE3-208 led to more than a 50% reduction in cell proliferation (Ki-67) and microvessel density (CD-34). These findings provided the rationale for complementary in vitro studies to further characterize the growth inhibitory effects of ONO-AE3-208. Neither treatment with exogenous PGE 2 nor the EP 4 RA altered the growth of 1483 cells in culture. Human endothelial cells were employed to begin to define the anti-angiogenic properties of the EP 4 RA. Treatment with 0-100 nM ONO-AE3-208 caused dose-dependent suppression of endothelial capillary tube formation. Taken together, these results suggest that the EP 4 receptor plays a significant role in mediating the growth promoting effects of PGE 2 in experimental HNSCC. Decreased tumor cell proliferation in xenografts may be a consequence of the anti-angiogenic effects of the EP 4 RA. Therapies that target PGE 2 synthesis or EP receptor antagonists may be useful in the treatment of malignancies including HNSCC.